Cent. Eur. J. Geosci. • 1(1) • 2009 • 19-32
DOI: 10.2478/v10085-009-0006-7
Central European Journal of Geosciences
On the occurrence of a pumice-rich layer in Holocene
deposits of western Peloponnesus, Ionian Sea,
Greece. A geomorphological and geochemical
approach.
Research Article
George D. Bathrellos, Charalampos Vasilatos, Hariklia D. Skilodimou, Michael G. Stamatakis∗
National and Kapodistrian University of Athens, 15784, Zografou, Athens, Greece
Received 7 November 2008; accepted 18 February 2009
Abstract: A single, pumice-rich sandy horizon located in Holocene deposits of western Peloponnesus, Ionian Sea, Greece
has been newly detected in a littoral belt 250 m wide and more than 3km long. Pumice fragments are hosted
in siliceous-cherty sand that overlies coarser clastic sediments, and occur in varying sizes. The geomorphology
of the area and the development of two dune systems played an important role in the entrapment of the pumice
fragments. These were transported there by the wind and marine currents, rather than by a tsunami event. The
chemistry of the pumice fragments is constistent throughout the deposit. Major and trace element analysis of the
pumice suggests an origin in the south Aegean Volcanic Arc, rather than in southern Italy and surroundings. The
age of this deposition is thought to be younger than 4,000 years before present.
Keywords: pumice • coastal zone • dune systems • surface currents • geochemistry
© Versita Warsaw
1. Introduction
Pumice is a vesicular, volcanic rock with a predominantly
glassy matrix. It is formed by mostly explosive eruptions
of viscous, gas-rich magma. It has a low specific gravity
due to its highly vesicular structure. In Greece, enormous pumice deposits occur in Thera Island, in the KosNissyros-Yali volcanic system, and in Milos and Kimolos islands [1]. In Milos and Kimolos islands, besides
the thick pumice flows, pumice fragments occur dispersed
in tuffaceous and biogenic sedimentary rocks. For ex∗
E-mail: [email protected]
ample, pumice fragments are found in the tuff/diatomite
sequence of Sarakiniko and Adamas Bay, Milos Island,
where pumice boulders and gravels of up to 3m in diameter have been sunk in Pliocene diatomite layers [2, 3].
Pumice pieces of up to 5cm in size also occur in many
beaches around the Greek coastlines of the Aegean Sea.
Pumice is the main product of all large volcanic eruptions
that are driven by the exsolution of water from gas-rich
magma. Among the best known examples are those of the
∼1470 BC eruption of Thera Island, the AD79 eruption
of Vesuvius and the 1883 eruption of Krakatau. Pumice
differs from all other volcanic rocks in its ability to float on
water due to its low bulk density, commonly in the range
of 0.5-0.7 gm/cm3 . Therefore, it can be transported by
marine currents and wind over large distances, regardless
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On the occurrence of a pumice-rich layer in Holocene deposits of western Peloponnesus, Ionian Sea, Greece. A geomorphological and
geochemical approach.
of the size of the pumice fragments.
Opportunities for the observation of floating pumice in
large quantities are relatively uncommon, because large
pumice-forming eruptions are infrequent, and the floating
pumice is fragile and subject to rapid attrition. The most
significant accumulations of floating pumice were those
resulting from the 1883 eruption of Krakatau. After the
eruption, floating pumice covered a large area of the Indian Ocean for several months. Some pumice was washed
ashore as far away as the coast of South Africa [4, 5] discussed the probability that pumice flows emitted by a volcano in a marine environment can travel coherently across
the surface of the sea. They found evidence that certain
pumice flows from the Krakatau eruption travelled 80 km
across open water before being deposited on the coast
of Sumatra. The occurrence of deep water between Kos
and the adjacent islands led [6] to propose that ignimbrite
Figure 1.
deposits resulted from pyroclastic flows that crossed wide
areas of open water.
In our area of study in the Eastern Mediterranean, volcanic activity of Neogene through recent times has been
primarily reported in the Aegean Sea and Western Anatolia. Volcanic activity of the same age has also been
reported in southern Italy and the adjacent islands (e.g.
Aeolian islands).
The Aegean Sea is bounded to the south by the South
Aegean volcanic arc, which includes the Pliocene to recent volcanic centres of Soussaki, near Corinth to the
west, Aegina Island, Methana peninsula and Poros Island, Milos-Kimolos- Polyegos islands, Thera Island, and
Kos-Nissyros-Yali islands (the easternmost) [7, 8]. Very
large subaerial pumice deposits are present on Nissyros,
as well as the island of Kos and the islet of Yali close to
the north.
Location of the study area.
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George D. Bathrellos, Charalampos Vasilatos, Hariklia D. Skilodimou,
Michael G. Stamatakis
Further west, the island of Thera is thickly covered with
pumice produced during the ∼ 1470 BC ”Minoan” eruption. Smaller pumice deposits found on the western part of
Kimolos Island thin towards Milos Island to the southwest.
However, there are other pumice fragment deposits along
the coastlines of the southern Aegean in Milos, Anafi, and
Crete islands [9–15]. These are not associated with local
volcanic activity, and may represent flotation deposits.
sia, Greek) issued by the institute of Geological and Mineral Exploration [16]. Fieldwork included identification of
the deposits of the coastal zone and collection of representative samples from the pumice horizon.
The purpose of the present study is to investigate the nature, origin and emplacement of a newly identified pumice
horizon found in Holocene deposits in the coastal zone of
western Peloponnesus.
Five samples were collected from the pumice-rich sandy
horizon, over a distance of 1 km, parallel to the seashore
and about 100 m landwards. Pumice pebbles ranging in
size between 0.2 cm and 6 cm were extracted by hand from
the horizon, which is unconsolidated sand that contains
primarily chert and grain sizes <1 cm.
The pumice pebbles collected were washed-out by deionized water to avoid any contamination by clay minerals
and seawater-derived evaporite salts, mainly sodium chloride.
Mineralogical, textural and microprobe analysis of the
pumice pieces were performed using thin sections, optical microscope, and scanning electron microscope at the
National and Kapodistrian University of Athens Geology
Department laboratories (JEOL JSM-5600 equipped with
Oxford Link ISIS 300 Energy Dispersive microprobe analytical system, beam current: 0.5 nA and diameter 2 μm).
For chemical analysis first the samples were cleaned with
distilled water in an ultrasonic bath. They were then dried
for 48 hours at ∼70°C, and homogenized by grinding in
an agate mortar to a grain size <100 μm.
Major and trace element chemical analysis of the bulk
pumice samples was implemented by ME - XRF06 (major elements) and ME - MS81 (trace and rare earth
elements) methods in the laboratories of Chemex Labs,
Saskatchewan, Canada.
2.
Regional settings
The study area is located in the western coastal zone
of Peloponnesus, Ionian Sea (Figure 1). More specifically, it is situated in the central part of the coastal zone
of Kyparissia Neogene-Quaternary basin. The coastline
is an undulating lowland made up of Holocene coastal
sandy deposits. The pumice-rich horizon identified forms
a zone of 230 m width and more than 3 km north to south.
This layer is interbedded with siliceous sand and gravel.
The drainage network is poorly developed and comprises
streams with seasonal flow that end up to Kyparissaikos
Gulf.
The geological structure of the region comprises alpine
and post-alpine formations [16]. Chert, flysch and limestones of the Olonos - Pindos zone form the alpine formations in the eastern part of the studied area. The postalpine formations from the oldest to the most recent are:
Pliocene conglomerates, sandstones and marls, Pleistocene terra-rossa, sand and pebbles, alluvial deposits
consisting of sand, pebbles, loam, fluvial deposits and terraces, and finally Holocene dunes and coastal sand. The
Holocene dunes and coastal sands are the only deposits
found in the studied area. The western Peloponnesus area
has been affected by faults of E-W and NNW-SSE directions, and demonstrates steady state uplift [16–18].
The climate in the area is typical Mediterranean with a
rainy period from October to May. The Kyparissaikos Gulf
is affected by winds from NW, W, SW, and S directions
which generate waves with maximum heights of more than
5 m [19].
3.
Materials and methods
The present study was made using the 1: 50,000 topographic map of the area (Hellenic Geographical Military
Service) and the 1:50,000 geological map (sheet Kyparis-
3.1. Sample preparation and analytical techniques
4. The geomorphology of the
coastal zone and the pumice horizon location
Two different coastal landforms were observed in the study
area: a wind-formed sandy beach, and a coastal dune field
(Figure 2). The beach has gentle slopes (< 5%) and is
composed of Holocene deposits. The beach-sand is mainly
siliceous, consisting of rounded, white quartz grains and
angular, brown chert grains. Less commonly, limestone
pebbles and gravels occur, which come from the erosion of
the neighboring alpine formations.
The dune formations are developed all along the coast.
Two systems of successive dune ridges running parallel
to the coastline were recognized. The profile of the dune
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On the occurrence of a pumice-rich layer in Holocene deposits of western Peloponnesus, Ionian Sea, Greece. A geomorphological and
geochemical approach.
Figure 2.
Stabilized old series of dunes (bottom left). The sandy terrain that contains the pumice pebbles is exposed in front
of it. Sea front is in the distance.
beach is shown in Figure 3. The most recent dune system
is extended close to the present coastline and has a height
of up 2.5 m and width of up 4 m. Poorly developed vegetation such as halophile bushes are colonized on these
dune formations.
Figure 3.
5.
The old dune system has a height of up 1.5 m and a width
of 20 m. It has been stabilized and covered by shrubs and
pine trees landwards. The two systems are separated by
elongated flat swale that has a width of up to 170 m (Figure 4). In the swale area landwards, a pumice-bearing
horizon of 10 cm was found at a depth of 30 cm below the
sand. Besides the sand, the pumice horizon contains well
rounded and mostly flattened pumice pebbles with a size
0.2 cm to 6 cm in diameter (Figure 5) and, rarely, bivalve
shells (pectinidae). Angular pumice fragments also occur
sporadically. The horizon has well defined stratigraphic
boundaries as the under- and overlying formations are
barren of pumice particles (Figure 6 and 7). The overlying formation is siliceous sand, whereas the underlying
formation consists of a gravel bed that has a thickness of
30 cm. It contains angular chert fragments up to 5 cm, and
well-rounded limestone pebbles up to 10 cm in diameter
derived from the Mesozoic substrate. Based on the gravel
morphology and the absence of fossil traces the gravel bed
is most likely of fluvial origin. Below the gravel bed fine
grained sand is developed for more than 1 m (Figure 8).
Schematic cross-section of the sedimentary formations and morphology of the studied area.
Mineralogy of the pumice
5.1. Light microscopy
acterized by the predominance of volcanic glass, and by
the presence of plagioclase, quartz, biotite and, opaq minerals. Plagioclase crystals are commonly idiomorphic,
fragmented, isolated in the glassy matrix or sometimes
The pumice pieces have a vesicular texture and fluidal
structure. The mineralogy of the pumice pebbles is char22
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George D. Bathrellos, Charalampos Vasilatos, Hariklia D. Skilodimou,
Michael G. Stamatakis
Figure 4.
Figure 5.
Figure 6.
The pumice-bearing sandy horizon. Note the slight difference of the fine-grained overlying the pumice horizon
sand and the coarse-grained underlying sand deposits. A
bivalve shell has sunk in the sand (middle-right).
Figure 7.
Secondary (reworked) deposit of pumice pebbles on the
present sand surface, due to local agricultural activities.
Figure 8.
Sedimentological column of the studied Holocene deposits
of Kyparissaikos Gulf.
The old dune system pictured from the west. The hill in
the distance is composed from alpine formations.
The appearance and size of the pumice fragments in the
studied area.
forming aggregates. Alteration of plagioclase to sericite,
and substitution by neoformed calcite, was also detected.
Authigenic calcite also occurs as vein fillings, pebble encrustation and rimming, or by the pumice pores forming
idiomorphic crystal aggregates. Quartz mostly forms aggregates of small allotriomorphic crystals hosted in the
glassy matrix.
5.2. SEM analysis
The fabric of the pumice is fluidal with rope texture. Timagnetite, zircon, rutile and pyroxene crystals were determined using the SEM, in addition to the glass, plagioclase, quartz and biotite that were detected by light
microscopy.
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On the occurrence of a pumice-rich layer in Holocene deposits of western Peloponnesus, Ionian Sea, Greece. A geomorphological and
geochemical approach.
6. Chemistry of the pumice
Table 2.
As shown in Tables 1 and 2, the chemistry of the pumice
pebbles is acidic. Summary major-element data for this
are listed in Table 1. The trace-element content of the
pumice samples is shown in Table 2. The measured loss of
ignition (LOI) of the samples is 4.81-4.95%. The chemical
analysis of the samples as well as the binary diagrams of
the oxides show that the pumice is homogeneous (Table 1).
Table 1.
Method
Samples DUN1 DUN2 DUN3 DUN4 DUN5 ME-MS81 LOR*
Ba
Ce
Co
Cs
Dy
Er
Eu
Ga
Gd
Hf
Ho
La
Lu
Nb
Nd
Pb
Pr
Rb
Sm
Sr
Ta
Tb
Th
Tm
U
V
W
Y
Yb
Zn
Zr
Major element analysis of pumice pebbles, Kyparissaikos
Gulf (values in %).
Method
Samples DUN1 DUN2 DUN3 DUN4 DUN5 ME-XRF06 LOR*
SiO2
TiO2
Al2 O3
Fe2 O3
MnO
MgO
CaO
Na2 O
K2 O
P2 O5
LOI
Total
69.48
0.12
13.42
1.69
0.1
0.25
1.4
4.07
3.95
0.02
4.95
99.45
69.28
0.12
13.36
1.66
0.09
0.25
1.36
4.11
3.94
0.02
4.84
99.03
69.39
0.11
13.42
1.66
0.09
0.24
1.37
4.08
3.96
0.03
4.81
99.16
69.57
0.10
13.4
1.67
0.1
0.25
1.38
4.08
3.94
0.02
4.88
99.39
69.32
0.11
13.37
1.68
0.1
0.24
1.39
4.1
3.95
0.03
4.87
99.16
Trace element analysis of pumice pebbles, Kyparissaikos
Gulf (values in ppm).
0.01
0.01
0.01
0.01
0.01
0.01
0.01
0.01
0.01
0.01
0.01
*LOR = limit of reporting
455
57
1.5
2.6
3.4
2.5
0.5
15
3.6
4
0.8
30.7
0.5
18
19.6
18.0
5.8
107.5
3.5
71.6
1.5
0.6
14
0.4
3.2
11.0
6
27.9
3.0
49
122.0
451
57
1.0
2.7
3.3
2.4
0.5
15
3.4
4
0.7
30.6
0.5
18
19.2
17.0
5.9
108.0
3.5
71.3
1.6
0.6
14
0.4
3.2
9.0
6
26.2
2.8
47
120.5
460
59
1.0
2.7
3.6
2.5
0.5
16
3.7
5
0.8
31.6
0.5
18
20.3
14.0
6.0
112.0
3.6
72.4
1.6
0.6
14
0.4
3.3
8.0
3
27.0
2.9
51
135.5
456
58
1.5
2.6
3.4
2.5
0.5
15
3.5
4
0.7
30.9
0.5
17
19.7
15.0
5.9
109.0
3.5
71.5
1.6
0.6
13
0.4
3.2
10.0
4
26.8
2.9
50
125.2
457
59
1.5
2.7
3.5
2.5
0.5
16
3.7
5
0.8
31.5
0.5
18
20.3
14.0
6.0
107.0
3.6
72
1.5
0.6
14
0.4
3.3
9.0
5
27.1
3.0
49
127.0
0.5
0.5
0.5
0.1
0.1
0.1
0.1
1.0
0.1
1.0
0.1
0.5
0.1
1.0
0.5
0.2
0.1
0.2
0.1
0.1
0.5
0.1
1.0
0.1
0.5
5.0
1.0
0.5
0.1
5.0
0.5
*LOR = limit of reporting
The SiO2 content of the pumice samples varies from 69.28%
to 69.57% (Figure 9), and is higher than the pumices derived from Vesuvius [23]. Similar silica content of pumice
fragments has been reported in tephra layers in core samples from the Tyrrhenian Basin [24] and in some volcanic
rocks from Pantelleria, Stromboli and Etna [25].
The TiO2 content in the pumice varies from 0.10% to 0.12%,
the CaO content ranges from 1.37% to 1.40% and the total
K2 O+Na2 O content ranges from 8.02% to 8.05% (Table 1).
The plots of the samples in the rock classification diagram
of [26, 27], have shown that they are of rhyolitic composition (Figures 10 and 11).
The [28] Alk(Na2 O+K2 O) – MgO – FeOt diagram (Figure 12) suggest a calc-alkaline origin and the SiO2 Alk(Na2 O+K2 O) (Figure 13) diagram shows sub alkaline
origin.
7.
Discussion
7.1. The origin of the pumice fragments from
chemical evidence
In the Eastern Mediterranean there are several possible
sources of pumice, either in the Aegean Sea and surroundings, or in southern Italy and surroundings. According to
the chemistry and location of the samples in the diagrams
of Figures 12 and 13, it is unlikely that they were derived
from the westernmost sites, such as the peralkaline rocks
reported in Pantelleria volcano [25].
The TiO2 and CaO content (Table 1) is lower than the
range of the rhyolitic tephra layers found in cores in the
central Tyrrhenian basin reported by [24]. For example,
the Mt. Etna lavas of the past few centuries show consistent characteristics; they are slightly evolved in terms
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Michael G. Stamatakis
Figure 9.
Diagrams of SiO2 versus major and trace elements.
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On the occurrence of a pumice-rich layer in Holocene deposits of western Peloponnesus, Ionian Sea, Greece. A geomorphological and
geochemical approach.
- Kyparissiakos pumice samples;
- Etna-SET2 lava sample from [22]
- Santorini pumice samples from [20]
- Vesuvius pumice sample from [23]
- Knosos pumice samples from [11]
- Stromboli lava flow sample from [21]
- Alicudi lava flow sample, from [21]
Figure 9.
Continued.
of the alkaline series (trachybasalts, also called hawaiites,
with 3-6% MgO), with low SiO2 content [29, 30].
The Rb/Sr (Figure 14) and Ba/K2 O diagrams (Figure 15)
show significant difference from the calc alkaline rocks
of the Aeolian Arc, Southern Tyrrhenian Sea [31]. It is,
therefore, extremely unlikely that our pumice fragments
from the Kyparissia Gulf have been transported from the
volcanic centers to the west.
Significantly, the Rb vs Sr (Figure 16) (LOG) and K/Rb
vs K2 O diagrams (Figure 17) shows similarity to volcanic
rocks from the Aegean Volcanic Arc. According to [32]
measurements, the pumices exhibit chemical similarity
with the volcanic rocks of Milos, but not to those of Thera.
Comparing the Nb/Zr vs La/Yb diagrams of the samples
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George D. Bathrellos, Charalampos Vasilatos, Hariklia D. Skilodimou,
Michael G. Stamatakis
Figure 10.
Figure 11.
Total alkali versus silica (TAS) diagram based on [26].
Zr/TiO2 versus Nb/Y diagram [27].
(Figure 18) with the systematic presented by [33], the
pumices fall between samples from Milos, Nissiros, the
Yali (Aegean Arc) area and the Aeolian arc area. In the Zr
vs SiO2 (percentage converted to dry basis), the pumices
plotclose to those from Milos, Nisiros and Yali (Aegean
Arc)
Figure 12.
(Na2 O+K2 O) – MgO – FeOt diagram [28].
Figure 13.
SiO2 - (Na2 O+K2 O) diagram [28].
7.2. Controlling factors of coast geomorphology
One of the characteristics of the studied area is the development of the coastal dunes in two systems parallel to
the coastline. The formation of the dunes is mainly due to
the action of strong winds that blow from the westerl and
southwester, as well as the gently-sloping beach and the
availability of sand.
According to [34] and [35], progradation of coastlines in
the NW Peloponnesus, north of the studied area, has most
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On the occurrence of a pumice-rich layer in Holocene deposits of western Peloponnesus, Ionian Sea, Greece. A geomorphological and
geochemical approach.
Figure 14.
The Rb vs Sr diagram.
Figure 16.
Rb vs Sr plots on logarithmic scale.
Figure 15.
The Ba vs K2 O diagram.
Figure 17.
K/Rb vs K2 O diagram.
likely taken place since sea level reached its present level
approximately 6,000 ka. Moreover, [19] suggests that the
development of dune fields in central Kyparissaikos Gulf
occurred during the last 4,000 years.
The presence of the two dune systems indicates the
progradation of the coastline during the Holocene. The
removal of sand by the wind resulted in sediment accumulation on the beach. The beach is also supplied by
sediments derived from fluvial sources. Sand and gravel
could furthermore have been deposited by the transporta-
tion of detrital material by littoral drift.
The swale area between the two dune-systems is probably
related to an older coastline which prograded seawards.
The area has a flat morphology and most likely represents
a dried old lagoon. This area is partially covered by reddish unsorted soil formation of less than 20 cm thick. It is
concluded that the clayey components entrapped between
the two dune series have been derived from land that was
exposed to oxidising conditions.
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The predominance of the small sized pumice pieces, and
their polishing, can be explained by forces applied by wind
and waves. The chemical homogeneity of the samples analyzed is an indicator of a single source/single event for the
pumice transportation and deposition. In many sandy deposits on the coast of Greece single pieces of pumice occur
hosted in sandy matrix. The studied deposit is different,
representing a dense accumulation of pumice fragments,
interbedded with barren sand. This is therefore another
indicator that the pumice accumulation studied is a single depositional event. We hypothesize that deposition
of the pumice fragments occurred less than 4,000 years
ago, as the old dune system that acted as a barrier to
further landward transportation of the pumice fragments
which has been dated at 4,000 years before present [19].
7.4. Action of tsunamis or surface currents?
Figure 18.
Zr vs. SiO2 and Nb/Zr vs. La/Yb systematics [33].
7.3. A distinct pumice horizon - a single specific event - when?
The pumice-bearing sandy horizon contains unsorted, polished pieces of pumice of mostly <1 cm in size. Rarely,
larger, angular pieces of up to 5 cm occur. The calcification of the pumice vugs and pores detected under the Light
Microscopy suggests a fresh-water movement through this
horizon.
Currently, wells developed in the studied area, even
though close to the sea, yield fresh-water. This means
that groundwater caused the calcification of the pores.
Tsunamis are often triggered by earthquakes and sometimes produced by largescale sediment slumping offshore [36, 37]. They are occasionally produced by volcanic eruptions taking place in the sea. Large tsunamis
that resulted from the Krakatau eruption were responsible
for great destruction and loss of life. One of the possible
effects of a tsunami is to transport floating material inland. In the case of Krakatau eruption fishing boats and
even a small ship were carried inland. Rounded pumice
fragments have been found in numerous coastal exposures
related to tsunamis generated by major volcanic eruptions [38]. There is doubt concerning the recognition of
pure tsunami events in a single pumice pebbles deposit.
According to [10], pumice was deposited by a tsunami up
to 250 m a.s.l. on the Anafi Island, lclose to and SE of
Thera Island. However, [39] considered that this pumice
was deposited by air fall processes, not by a tsunami.
Moreover [15, 38, 40] controvert the hypothesis that in all
cases pumice deposits had been transported by tsunami.
According to [38] floating pumice has drifted on surface
currents throughout the Aegean and eastern Mediterranean Seas. They suggest that pumice deposits along
the Levant coastline were deposited by surface currents,
not by tsunamis generated by a Holocene eruption of Santorini.
As the Kyparissia Gulf pumice horizon is located close to
the present coastline and not significantly higher above
sea level, it seems likely that it was deposited by flotation
alone, and not by the action of a tsunami event.
The pumice fragments were probably generated by a
paroxysmal volcanic event in the Aegean Sea. They then
travelled by surface currents through the Aegean and Ionian seas and were deposited on the western beaches of
Peloponnesus. The directions of the surface currents in
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On the occurrence of a pumice-rich layer in Holocene deposits of western Peloponnesus, Ionian Sea, Greece. A geomorphological and
geochemical approach.
Figure 19.
The directions of surface currents during the winter in Aegean and Ionian Sea (modified from [41]).
Figure 20.
The directions of surface currents during the summer in Aegean and Ionian Sea (modified from [41]).
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Aegean and Ionian seas are shown in Figures 19
and 20 [41]. According to the directions of surface currents during winter and summer (mainly SW and S), it is
plausible that the floating pumice was transported from
the Aegean Sea to the Ionian Sea. As the currents are
coming from the southwest or west (seawards), the pumice
fragments were deposited at the locations where they are
presently found.
8.
Conclusions
The morphology of the area and the development of two
dune systems played an important role in the entrapment
of the pumice fragments that were arrived there with the
action of the surface currents rather a tsunami event.
The chemistry of the pumice fragments is in accordance
with an origin in the southern Aegean Volcanic Arc, rather
than southern Italy and its surroundings. The age of
this deposit is thought to be less than 4,000 years before present.
Acknowledgments
Thanks are expressed by the authors to George Stamatakis, chemist for helping in fieldwork.
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